I. Field of the Invention
The present invention relates generally to a fuel delivery system for an internal combustion engine.
II. Description of the Prior Art
In conventional gasoline fueled internal combustion engines of the type used in the automotive industry, a manually actuated throttle body is fluidly disposed in series with the intake manifold upstream from the engine combustion chamber(s). This manually controlled throttle is mechanically linked to the accelerator pedal in the automotive vehicle such that depression and release of the accelerator pedal respectively opens and closes the throttle plate of the throttle valve. The opening and closure of the throttle plate within the intake manifold, of course, controls the mass air flow rate through the intake manifold.
While the previously known manually actuated throttles for internal combustion engines have operated satisfactorily during high engine RPM operating conditions, such manually controlled throttles have been inadequate by themselves to control the air flow rate to the internal combustion chambers of the engine during an idle and/or cold start operating condition. The inability of the manually actuated throttles to control the air flow rate during an idle and/or cold start engine operating condition arises primarily through government emission standards which require increasingly lower levels of noxious emissions from the engine during all engine operating conditions, including both idle and cold start operating conditions.
In order to rectify this inadequacy of the manually controlled throttles for internal combustion engines, it has been the previous practice to provide a bypass passageway around the manual throttle such that the bypass passageway includes an inlet upstream from the manual throttle and an outlet downstream from the manual throttle. Thus, during both idle and cold start operating conditions, the air flow to the engine is provided through the bypass passageway, rather than the main intake manifold.
In order to control the air flow through the bypass passageway during both idle and cold start operating conditions, these previously known fuel delivery systems have utilized an idle speed control valve fluidly connected in series with the bypass gas flow passageway. A typically microprocessor based engine control unit (ECU) then controls the actuation of the idle speed control valve between its fully closed and fully open position to accordingly vary the gas flow through the bypass gas flow passageway. Typically, these idle speed control valves are linear valves and thus may be variably opened between their fully closed and fully open positions.
In order to accurately control the fuel/air mixture to the engine during a cold start operating condition, it has also been previously known to provide a cold start fuel injector within the bypass passageway. This cold start fuel injector provides fuel to the engine in lieu of the multi-point fuel injectors utilized during a cold engine condition. The use of the cold start fuel injector enables accurate control of the fuel/air mixture by the ECU during the cold start operating condition thereby minimizing noxious emissions from the engine. Additionally, many of these cold start fuel injectors include heating elements of one sort or another positioned within the bypass passageway to enhance the vaporization of the fuel in the bypass passageway and prior to its introduction into the internal combustion engine for better fuel economy, better engine efficiency and reduced noxious emissions.
One disadvantage, however, of utilizing both a manually operated throttle as well as the idle speed control valve is that the idle speed control valve necessarily increases the overall cost of the fuel delivery system above the use of a manually controlled throttle by itself. However, it has been previously necessary to utilize an idle speed control valve in combination with a manually actuated throttle in order to meet government emission standards.
In recent years, electronically controlled throttle valves have been introduced in which the actuation of the throttle valve, typically a throttle plate in the intake manifold, is controlled by an electric motor. The ECU, in turn, controls actuation of the electric motor in response not only to electronic sensors associated with the accelerator pedal for the vehicle, but also in response to various engine operating conditions and engine parameters. Since the ECU is capable of accurately controlling the degree of opening or closure of the throttle during all engine operating conditions, the electronically controlled throttle valve is able to replace both the previously used manual throttle valve as well as the idle speed control valve. The utilization of electronically controlled throttle valves not only achieves low engine emissions but also better traction control and vehicle cruise control.
In order to achieve the accurate control of air flow through the intake manifold necessary to meet governmental emission standards, it has been necessary to manufacture the electronically controlled throttle valve with its associated throttle body to a high degree of accuracy. This, in turn, has increased the overall manufacturing cost of the electronically controlled throttle valve and its associated body. Furthermore, it is difficult to maintain this high degree of accuracy for the electronically controlled throttle valve and its associated body over the useful life of the internal combustion engine.